Seatbelt pretensioning retractor assembly including a piston-safety valve member

ABSTRACT

A seatbelt pretensioning retractor assembly for use in a passenger vehicle is provided. The pretensioning assembly includes a tube in fluid communication with a gas generator and a driving element disposed therein that travels in a first direction in response to actuation of the gas generator. The driving element includes a polymer rod. A stopper is coupled to a proximal end portion of the polymer rod. A piston-safety valve member is disposed between the gas generator and the stopper and is configured to allow gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure.

TECHNICAL FIELD

The technical field relates generally to seatbelt restraint devices for restraining an occupant of a vehicle, and more particularly, to devices for pretensioning a seatbelt.

BACKGROUND

Seatbelt restraint systems for restraining an occupant in a vehicle seat play an important role in reducing occupant injury in vehicle crash situations. Seatbelt restraint systems of the conventional so-called “3-point” variety commonly have a lap belt section extending across the seat occupant's pelvis and a shoulder belt section crossing the upper torso, which are fastened together or are formed by a continuous length of seatbelt webbing. The lap and shoulder belt sections are connected to the vehicle structure by anchorages. A belt retractor is typically provided to store belt webbing and may further act to manage belt tension loads in a crash situation. Seatbelt restraint systems which are manually deployed by the occupant (so-called “active” types) also typically include a buckle attached to the vehicle body structure by an anchorage. A latch plate attached to the belt webbing is received by the buckle to allow the belt system to be fastened for enabling restraint, and unfastened to allow entrance and egress from the vehicle. Seatbelt systems, when deployed, effectively restrain the occupant during a collision.

OEM vehicle manufacturers often provide seatbelt restraint systems with pretensioning devices, which tension the seatbelt either during an impact of the vehicle or even prior to impact (also known as a “pre-pretensioner”) to enhance occupant restraint performance. The pretensioner takes out slack in the webbing and permits the belt restraint system to couple with the occupant early in the crash sequence. One type of pretensioner acts on the webbing retractor to tension the belt. Various designs of retractor pretensioners presently exist, including a type known as a roto-pretensioner that incorporates a gas generator for generating a pyrotechnic charge. Examples of such roto-pretensioners are described in U.S. Pat. No. 5,881,962, filed Apr. 11, 1995, U.S. Patent Application Publication No. 2006/0243843, filed Apr. 27, 2005, U.S. Patent Application Publication No. 2012/0006925, filed Jul. 6, 2010, and U.S. Pat. No. 7,988,084, filed Aug. 2, 2011, which are commonly owned by the assignee of the present application and are hereby incorporated by reference in their entirety for all purposes. Generally, ignition of the pyrotechnic charge or other combustible material creates gas pressure in a chamber having a piston to impart motion upon a driving element such as a piston, rack and pinion, or series of balls disposed in a pretensioner tube, which engage with and wind a retractor spool sprocket to retract the webbing.

One issue with pretensioners using a series of metallic balls is the weight of the series of balls required for a full pretensioning stroke, as well as the corresponding cost of supplying multiple metallic balls with strict tolerances. Further, for pretensioners using a series of metallic balls, or rack and pinion based systems, is the need for a synchronizing or clutch feature to ensure that the series of balls or pinion sufficiently engage the retractor spool sprocket.

Another issue with pretensioners is known as a low resistance condition, where the driving elements will reach an end of stroke without experience substantial resistance. This can occur if there is excessive slack in the seatbelt webbing. In these cases, the low resistance results in a lower amount of backpressure from the driving elements. The backpressure is produced by the engagement between the driving elements and the sprocket, so lower backpressure reduces the pressure on a sealing element that trails the driving elements. Reduced pressure on the sealing elements reduces the amount that the sealing element is compressed circumferentially. Reduced sealing ability can cause gas to leak from the tube around the series of balls.

A further issue with pretensioners is the need to maintain the retractor and the seatbelt webbing in a locked condition at the end of the pretensioning stroke. When the retractor spool does not remain locked, payback can occur which allows the seatbelt to unspool and reintroduce slack in the seatbelt. One method for maintaining the locked position includes maintaining pressure from the gas generator beyond the amount needed for the pretensioning stroke. However, this adds weight and cost.

Another issue with pretensioners is the need to vent gas to prevent or in the event of an overpressure condition. This can occur, for example, when the gas generator is deployed and the retractor spool for some reason cannot pretension and the driving elements experience substantial resistance as they attempt to advance toward an end of the pretensioning stroke. This can cause a substantial increase in the pressure of expanding gas from the gas generator that is attempting to push the driving elements.

BRIEF SUMMARY

Seatbelt pretensioning retractor assemblies for use in a passenger vehicle are provided herein. In an exemplary embodiment, a seatbelt pretensioning retractor assembly includes a housing that is adapted for being mounted to a vehicle structure. The housing has an interior cavity. A tube has an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing. A sprocket is rotatably mounted to the housing and is fixedly coupled to a spindle adapted for taking up seatbelt webbing during pretensioning. A driving element includes a polymer rod having a proximal end portion that is disposed towards the gas generator and a distal end portion that is opposite the proximal end portion. The polymer rod is configured to extend in a longitudinal direction from the proximal end portion to the distal end portion. The polymer rod is disposed within the tube and is translatable through the tube in a first direction toward the sprocket in response to an actuation by the gas generator. A stopper is coupled to the proximal end portion of the polymer rod. A piston-safety valve member is disposed between the gas generator and the stopper and is configured to allow gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure.

In another exemplary embodiment, a seatbelt pretensioning retractor assembly for use in a passenger vehicle is provided. The seatbelt pretensioning retractor assembly includes a housing adapted for being mounted to a vehicle structure and has an interior cavity. A tube has an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing. A sprocket is rotatably mounted to the housing and is fixedly coupled to a spindle adapted for taking up seatbelt webbing during pretensioning. The sprocket has a plurality of vanes. A driving element includes a polymer rod having a proximal end portion that is disposed towards the gas generator and a distal end portion that is opposite the proximal end portion. The polymer rod is configured to extend in a longitudinal direction from the proximal end portion to the distal end portion. The polymer rod is disposed within the tube and is translatable through the tube in a first direction toward the sprocket in response to an actuation by the gas generator. A stopper is coupled to the proximal end portion of the polymer rod. A piston-safety valve member is disposed adjacent to the stopper on a side opposite the proximal end portion of the polymer rod. The piston-safety valve member includes a piston body and a safety valve operatively coupled to the piston body. A seal member is disposed between the gas generator and the piston-safety valve member and has a through hole in fluid communication with the safety valve. The seal member and the piston-safety valve member cooperate to allow gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure.

Further objects, features, and advantages of the invention will become apparent to those skilled in the art to which the present invention relates from consideration of the following description and the appended claims, taken in conjunction with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is perspective view of an occupant restraint system in accordance with an exemplary embodiment;

FIG. 2 is a perspective view of the occupant restraint system with various components removed to show a seatbelt pretensioning retractor assembly in accordance with an exemplary embodiment;

FIG. 3 is a perspective view of the seatbelt pretensioning retractor assembly in accordance with an exemplary embodiment;

FIG. 4 is a cut-away view of the seatbelt pretensioning retractor assembly illustrating a tube, a polymer rod, and a sprocket in a non-actuated position in accordance with an exemplary embodiment;

FIG. 5 is a side cut-away view of the polymer rod and a stopper in accordance with an exemplary embodiment;

FIG. 6 is a plan view of the sprocket having a plurality of vanes in accordance with an exemplary embodiment;

FIG. 7 is a side view of the sprocket in accordance with an exemplary embodiment;

FIG. 8 is a partial view of the sprocket illustrating the shape of the vanes in accordance with an exemplary embodiment;

FIG. 9 is a cross-sectional view of the seatbelt pretensioning retractor assembly in an actuated position in accordance with an exemplary embodiment;

FIG. 10 is a cross-sectional view of the tube, a seal member, a piston-safety valve member, the stopper, and the polymer rod of the seatbelt pretensioning retractor assembly in accordance with an exemplary embodiment;

FIG. 11 is an exploded side view of the seal member, the piston-safety valve member, the stopper, and the polymer rod in accordance with an exemplary embodiment;

FIG. 12 is a cross-sectional view of the piston-safety valve member in accordance with an exemplary embodiment;

FIG. 13 is an exploded perspective side view of the piston-safety valve member in accordance with an exemplary embodiment;

FIG. 14 is a partial exploded perspective view of the tube, the polymer rod, and the stopper in accordance with an exemplary embodiment;

FIGS. 15A-15C are cross-sectional views of various embodiments of the tube and the stopper illustrated in FIG. 10 along line 15-15;

FIGS. 16A-16E are cross-sectional views of various embodiments of the polymer rod illustrated in FIG. 5 along line 16-16;

FIG. 17 is a cross-sectional view of an embodiment of a constriction portion in the tube;

FIG. 18 is a cross-sectional view of another embodiment of the constriction portion;

FIG. 19 is a cross-sectional view of another embodiment of the constriction portion;

FIGS. 20A and 20B are perspective views of the polymer rod in accordance with an exemplary embodiment; and

FIGS. 21A-21D are cross-sectional views of the piston-safety valve member, the stopper, and the proximal section of the polymer rod in accordance with various exemplary embodiments.

It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

DETAILED DESCRIPTION OF THE INVENTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure or its application or uses.

Referring now to the drawings, FIG. 1 shows a vehicle seat 10 and a seatbelt assembly 12 in accordance with an exemplary embodiment. The seatbelt assembly 12 includes a seatbelt webbing 14 having a shoulder belt portion 16 extending from an upper guide loop or anchorage 18 to a latch plate 20 and a lap belt portion 22 extending from the latch plate 20 to an anchorage 24. The latch plate 20 can include a loop portion 26 through which the seatbelt webbing 14 extends. The latch plate 20 is able to be inserted into a seatbelt buckle 28 to lock and unlock the seatbelt assembly 12. A seatbelt buckle cable 30, either directly or in cooperation with other components, secures the seatbelt buckle 28 to a portion 31 of the vehicle structure (e.g., vehicle frame). It will be appreciated that other manners of attaching the seatbelt webbing 14 to vehicle could also be used, including variations on the latch plate 20 and the seatbelt buckle 28 and their attachments to the seatbelt webbing 14 and associated vehicle structure.

The seatbelt webbing 14 is able to pay-out from a seatbelt pretensioning retractor assembly or retractor assembly 32 (shown in FIGS. 2 and 3), which is located within the vehicle seat 10 (in an integrated structural seat design) or is coupled structurally to the vehicle body, so that the effective length of the seatbelt webbing 14 is adjustable. When the latch plate 20 has been fastened to the seatbelt buckle 28, the seatbelt assembly 12 defines a three-point restraint between the anchorage 18, the latch plate 20, and the anchorage 24. Any other suitable configurations, such as alternative locations for the retractor assembly 32, the latch plate 20, and the anchorage 24, may be used with the present invention.

Now with reference to FIG. 2, an isometric view of the seatbelt assembly 12 is illustrated disassociated from the motor vehicle and showing the retractor assembly 32 in accordance with an exemplary embodiment. The retractor assembly 32 includes a spool assembly 34 and a gas generator 36 mounted to a common frame 38. The spool assembly 34 is connected with and stows the seatbelt webbing 14 of the shoulder belt portion 16, whereas the end of the lap belt portion 22 of the seatbelt webbing 14 is fixedly engaged with the anchorage point, for example, the frame 38 or another portion of the motor vehicle such as the seat 10 (shown in FIG. 1) or floor pan.

Referring also to FIG. 3, the spool assembly 34 includes a belt spool 40 that engages the shoulder belt portion 16 of the seatbelt webbing 14 and rotates to wind-up or pay-out the seatbelt webbing 14. A torsional “clock” or “motor” type spring is carried within a spring end cap 42 and rotationally biases the belt spool 40 to retract the seatbelt webbing 14. The spool assembly 34 may further incorporate other spool control mechanisms that are known in accordance with the prior art, including pretensioners, inertia and webbing sensitive locking devices, torsion bar load limiters, or other belt control devices. “Spool control systems” referred to in this specification may include any system that controls the rotational movement of a webbing spool, thus controlling the extraction and retraction of seatbelt webbing. One such spool control system is a motor-assisted retractor. Spool locking devices typically incorporate an inertia sensitive element, such as a rolling ball or pendulum, and cause a sprocket of the spool to be engaged to prevent further withdrawing of the seatbelt webbing 14 from the belt spool 40. Webbing sensitive locking devices sense rapid pay-out of seatbelt webbing 14 to lock the retractor assembly 32. Various electronic sensing mechanisms that detect the withdrawal of seatbelt webbing 14 and/or the connection of the latch plate 20 to the seatbelt buckle 28 may also be incorporated into the retractor assembly 32.

During normal operation of the vehicle, the retractor assembly 32 allows pay-out of seatbelt webbing 14 to give the occupant a certain amount of freedom of movement. However, if an impact or a potential impact situation is detected, the retractor assembly 32 is locked to prevent pay-out and to secure the occupant in the seat 10. For example, if the vehicle decelerates at a predetermined rate or if the brakes are actuated with a predetermined force, then the retractor assembly 32 is locked. Due in part to the free pay-out of the seatbelt webbing 14, the seatbelt assembly 12 often develops slack during normal use.

FIG. 4 provides a cut-away illustration of a pretensioner system 44 in accordance with an exemplary embodiment. Referring to FIGS. 3-4, in particular, the retractor assembly 32 further incorporates the pretensioner system 44 operatively connected to the spool assembly 34 and operable to rotate the belt spool 40 for pretensioning. As known to those of skill in the art, a retractor pretensioner winds seatbelt webbing into a more taught condition against the occupant at the initial stages of a detected vehicle impact. This is provided to reduce forward motion or excursion of the occupant in response to the deceleration forces of a vehicle impact or rollover.

The pretensioner system 44 includes a pretensioner tube 52 in communication with the gas generator 36. The gas generator 36 is used to provide expanding gas in response to a firing signal. As is known in the art, for example, the vehicle includes a sensor array sending a signal indicative of an emergency event such as an impact event, crash, or rollover. The vehicle sensor may be a specific impact sensor, or may be a traditional vehicle sensor (e.g. a longitudinal or lateral acceleration sensor) or otherwise part of a control system having a suite of multiple sensors. Any other impact sensor that is or will be known to those skilled in the art may also be readily employed in conjunction with the seatbelt assembly 12 of present invention. An electronic control unit such as a central processing unit (CPU) or other controller receives a signal and controls the seatbelt assembly 12 to respond by tightening the seatbelt webbing 14 of the vehicle (e.g. via activation of a pretensioner).

As will be discussed in further detail below, the pretensioner tube 52 has a pretensioner rod 53, e.g., a polymer rod or a plastically deformable polymer rod, disposed therein that has an elongate shape and is flexible within the tube 52. More specifically and as will be discussed in further detail below, the pretensioner rod 53, when disposed outside of the pretensioner tube 52 prior to insertion therein, has a generally straight shape, and when inserted into the tube 52 it will bend and flex in accordance with the tortuous shape of the tube 52.

Turning now to the retractor assembly 32, the retractor assembly 32 includes the spool assembly 34 mounted to the common frame 38, as described above. More particularly, the spool assembly 34 will rotate relative to the common frame 38 to wind the seatbelt webbing 14 attached to the spool assembly 34. The common frame 38 includes a housing 54 for housing the components of the pretensioner system 44.

The spool assembly 34 includes a sprocket 56 that is disposed within the housing 54. The sprocket 56 is attached to the belt spool 40. Rotation of the sprocket 56 will cause the attached belt spool 40 to rotate to wind the seatbelt webbing 14 that is attached to the belt spool 40.

FIG. 5 provides a side cut-away illustration of the pretensioner rod 53 and a stopper 55 in accordance with an exemplary embodiment. FIGS. 16A-16E provide cross-sectional views of various embodiments of the pretensioner rod 53 illustrated in FIG. 5 along line 16-16. As shown in FIGS. 5 and 16A-16E, the pretensioner rod 53 has a generally circular cross-section in one form. In another approach, the pretensioner rod 53 could have a non-circular cross-section, such as a generally rectangular cross-section, generally triangular cross-section, or other polygonal cross-section that allows the pretensioner rod 53 to be inserted into the pretensioner tube 52 (shown in FIG. 4) and adapt to the tortuous shape of the pretensioner tube 52 when inserted. For purposes of discussion, the pretensioner rod 53 will be discussed as having a generally circular cross-section

As illustrated and as discussed above, the pretensioner rod 53, when disposed outside of the pretensioner tube 52, has a generally straight shape and extends in a longitudinal direction 200 from a proximal end portion 202 to a distal end portion 204. The proximal end portion 202 is disposed towards the gas generator 36 (shown in FIG. 10) when the pretensioner rod 53 is installed within the pretensioner system 44. In an exemplary embodiment, the pretensioner tube 52 has a cross-section that varies along its length to define a non-recessed portion 206 and a recessed portion 208 that defines a recess 210. In one example and as illustrated in FIGS. 5 and 16D, the recess 210 is configured as a groove 212, e.g., U-shaped groove with sidewalls 214 a. In another example and as illustrated in FIG. 16A, the recessed portion 208 has a recessed ruled surface 214 b, e.g., substantially flat surface, which defines the recess 210. Non-limiting alternative examples of different forms of the recess 210 are illustrated in FIGS. 16B-16C and 16E.

Referring to FIG. 5, in an exemplary embodiment, the recessed portion 208 extends along a majority of the overall length of the pretensioner rod 53 from the proximal end portion 202 to and including the distal end portion 204. As illustrated, the proximal end portion 202 includes the non-recessed portion 206 in which the recess 210 terminates at a distal-most section of the non-recessed portion 206. As will be discussed in further detail below and as illustrated in FIGS. 5 and 16A-16E, the non-recessed portion 206 of the pretensioner rod 53 has a diameter, cross-sectional dimension, and/or perimeter greater than the recessed portion 208. In an exemplary embodiment, the non-recessed portion 206 has a length L1 of from about 15 to about 25 mm, such as about 20 mm and a width W1 of from about 4 to about 7 mm, and the recessed portion 208 has a length L2 of from about 60 to about 145 mm and a thickness W2 of from about 2.5 to about 8.0 mm.

In an exemplary embodiment, the pretensioner rod 53 also includes a positive feature 216, e.g., nub or post, extending proximally from the proximal end portion 202. The stopper 55 has a negative feature 218 formed therein that receives the positive feature 216 to couple the stopper 55 to the proximal end portion 202 of the pretensioner rod 53. In one example, the negative feature 218 and the positive feature 216 are sized such that the stopper 55 is compression fit, e.g., interference fit, onto the positive feature 216 to fixedly couple the stopper 55 to the pretensioner rod 53. Other forms of coupling and/or fixing the stopper 55 to the positive feature 216 and/or the proximal end portion 202 may be used, such as, for example, an adhesive, mechanical means, or the like. As illustrated in FIG. 5, the negative feature 218 can be configured as a blind hole 220.

In an exemplary embodiment, the pretensioner rod 53 is made from a polymer material, which has a reduced weight relative to metallic ball driving elements of other roto-pretensioners. The particular polymer material can be selected to fit the particular desires of the user. The polymer material is preferably one that has sufficient flexibility such that it can bend and flex through the pretensioner tube 52 to allow for initial installation as well as in response to actuation by the gas generator 36. The polymer material is preferably one that has sufficient pushability in response to actuation, such that the pretensioner rod 53 will sufficiently transfer a load to a sprocket 56 of the pretensioner system 44, thereby functioning as a driving element for causing pretensioning.

Further, in an exemplary embodiment, the pretensioner rod 53 is made from a polymer material that is plastically deformable. During and after actuation, the pretensioner rod 53 will be become plastically deformed in response to actuation and contact with other components (e.g., the sprocket 56) of the pretensioner system 44. As will be discussed in further detail below, this plastic deformation will cause the pretensioner rod 53 to become locked, for example, in the sprocket 56 to prevent or limit payback of the pretensioner rod 53 without being completely dependent on maintained pressure in the system.

In one approach, the pretensioner rod 53 is made from a nylon thermoplastic material. The pretensioner rod 53 could also be made from an aliphatic polyamide thermoplastic material. In another approach, the pretensioner rod 53 could be made from a similar thermoplastic material, such as an acetal material or polypropylene material.

With reference to FIGS. 6-8, the sprocket 56 has a general annular shape that defines an internal aperture 76. The sprocket 56 further defines a plurality of inward extending teeth 78 that extend into the aperture 76. The teeth 78 are sized and configured to correspond to recesses or depressions that are defined on an external surface of the belt spool 40 (shown in FIG. 3) to connect the sprocket 56 to the belt spool 40 such that they are rotationally coupled. In another approach, the internal aperture 76 could include a single tooth or protrusion to rotationally couple the sprocket 56 to the belt spool 40.

The sprocket 56 includes an annular body portion 80 and a flange portion 82 that projects radially from the base of the annular body portion 80. The sprocket 56 further includes a plurality of vanes 84 that each project radially from the annular body portion 80 as well as longitudinally from the flange portion 82, such that vanes 82 extend between the annular body portion 80 and the flange portion 82.

The vanes 84 each have a generally triangular shape when viewed from the front, with a base that tapers into a point 86 as the vane 84 extends radially outward from the annular body portion 80. The particular width and pitch of the vanes 84 can be selected as desired. The plurality of vanes 84 combine to define cavities 88 that are disposed between adjacent vanes 84.

In one approach, each of the vanes 84 can have the same size and shape and be uniformly distributed around the sprocket 56. In another approach, the vanes 84 can have different sizes and/or be spaced at different intervals. Adjusting the size and spacing of the vanes 84 can alter the amount of rotation and/or the rate of the rotation for the sprocket 84 when the pretensioner system 44 is activated. This variable size and/or spacing is possible due to the actuation by the pretensioner rod 53 rather than by a series of similarly shaped balls. In a pretensioner that uses a plurality of ball-shaped driving elements, the size and spacing is preferably uniform to account for the predetermined shape and size of the balls.

With reference once again to FIG. 4, the housing 54 further include a guide portion 90. The guide portion 90 is disposed within the housing 54 similar to the sprocket 56. More particularly, the guide portion 90 is disposed opposite an exit 89 of the tube 52, and the sprocket 56 is disposed between the guide portion 90 and the tube 52. Accordingly, the pretensioner rod 53 exiting the tube 52 will contact the sprocket 56 prior to contacting the guide portion 90.

The guide 90 has a generally arcuate landing surface 92 that has a concave shape toward the exit of the tube 52. In one approach, the arc of the surface 92 has a constant radius. Further, the center point of the radius of the arc is aligned with the rotational axis of the sprocket 56, such that the radial spacing between the surface 92 and the sprocket 56 is consistent along the length of the surface 92. In another approach, the center point of the radius of the surface 92 could be offset from sprocket axis, such that the radial spacing between the surface 92 and the outer diameter of the sprocket 56 will vary at different points along the surface 92.

The surface 92 includes a first end 96 and second end 98. The first end 96 is disposed opposite the exit 89 of the tube 52 such that the pretensioner rod 53 would engage the first end 96 prior to the second end 98 after exiting the tube 52 and passing the sprocket 56.

The housing 54 further defines an overflow cavity 100 that is disposed opposite the guide 90. The overflow cavity 100 is also disposed adjacent the curvature of the tube 52, and the sprocket 56 is disposed between the guide 90 and the overflow cavity 100. Accordingly, an intermediate portion 101 of the guide 90 is diametrically opposite the overflow cavity 100 across the sprocket 56.

The overflow cavity 100 is sized and configured to allow a portion the pretensioner rod 53 to be received therein during actuation of pretensioner system 44, if necessary. For example, after the pretensioner rod 53 has exited the tube 52 it will contact the guide 90 and be directed in an arcuate path corresponding to the guide 90, such that the pretensioner rod 53 is ultimately directed toward the overflow cavity 100. The pretensioner rod 53 can extend into the overflow cavity 100, and can further be guided along the curvature of the tube 52 that is adjacent the overflow cavity 100. However, it will be appreciated that the pretensioner rod 53 may not necessarily travel far enough during actuation to ultimately reach the overflow cavity 100.

As described above, the retractor assembly 32 includes the gas generator 36 that provides expanding gas in response to a firing signal. The expanding gas causes an increase in pressure within the tube 52, which ultimately causes the pretensioner rod 53 to be forced away from the gas generator 36, through the tube 52, and pass the exit 89 into the sprocket 56 for pretensioning.

More particularly, as shown in FIGS. 10-11, the pretensioner tube 52 includes piston-safety valve member 300 that is disposed adjacent to the stopper 55 opposite the pretensioner rod 53, and a seal member 102 that is disposed between the gas generator 36 and the piston-safety valve member 300. In an exemplary embodiment, the piston-safety valve member 300 and the seal member 102 are operatively coupled together and slidably disposed within the tube 52 to function as a piston during pretensioning to drive the pretensioner rod 53 along an actuating direction or path A through the tube 52 and into the sprocket 56. As will be discussed in further detail below, to prevent or in the event of an overpressure condition during pretensioning, however, the piston-safety valve member 300 and the seal member 102 cooperate to allow gas from the gas generator 36 to pass therethrough when the gas is at or above a predetermined pressure. It should be noted however that although the various embodiments disclosed herein described the seal member 102 and the piston-safety valve member 300 cooperating to function as a piston, it is to be appreciated by those skilled in the art that it is within the scope of the present disclosure that the piston-safety valve member 300 may function independently as a piston without the seal member 102, for example, by modifying the piston-safety valve member 300 to additionally provide a sealing feature with the interior wall of the tube 52. For example, the piston-safety valve member 300 may be formed of a relatively flexible material that may circumferentially expand against the interior wall of the tube 52 during pretensioning due to pressure from the gas from the gas generator 36, and/or the outer surface of the piston-safety valve member 300 may be designed to be near a net fit with the interior wall of the tube 52 to substantially prevent the gas from advancing past the piston-safety valve member 300 between the outer surface of the member 300 and the interior wall of the tube 52.

Referring to FIGS. 10-13, in an exemplary embodiment, the piston-safety valve member 300 includes a piston body 302 and a safety valve 304 operatively coupled to the piston body. In one example, the diameter or dimensions that define the outer surface of the piston body 302, which may be cylindrical in shape or otherwise, are sized slightly smaller than the width of the tube 52 to facilitate the piston-safety valve member 300 translating through the tube 52.

The safety valve 304 includes a safety valve diaphragm 306 and a lip insert 308 that interfaces with the stopper 55. The safety valve diaphragm 306 is disposed between the piston body 302 and the lip insert 308. In particular, the piston body 302 has a wall 309 that defines a body opening 310 (e.g., a through hole) and that includes a step or shoulder portion 311 at least partially surrounding the body opening 311. The body opening 310 is in fluid communication with the safety valve diaphragm 306.

Likewise, the lip insert 308 has a lip insert opening 312 (e.g., a through hole) formed therethrough that is in fluid communication with the safety valve diaphragm 306 on a side opposite the body opening 310. As illustrated, the safety valve diaphragm 306 is “cup-shaped” with a sidewall 314 that surrounds a central diaphragm portion 316. The safety valve diaphragm 306 is disposed between the shoulder portion 311 of the piston body 302 and the lip insert 308 with the sidewall 314 disposed on the shoulder portion 311 and the central diaphragm portion 316 extending across the body opening 310. As such, when fully intact, the central diaphragm portion 316 of the safety valve diaphragm 306 provides a seal or otherwise obstructs fluid communication between the body opening 310 and the insert opening 312. As will be discussed in further detail below, to prevent or in the event of an overpressure condition, the central diaphragm portion 316 of the safety valve diaphragm 306 ruptures at a predetermined pressure, thereby breaking the seal to allow fluid communication from the body opening 310 to the insert opening 312.

As illustrated, the lip insert 308 has a lip portion 318 that contacts the stopper 55 along an interface 320. The lip insert 308 has channels that are formed along the lip portion 318 that allow fluid (e.g., gas from the gas generator 36) to advance from the lip insert 308 (e.g., the insert opening 312) downstream past the interface 320 and along the exterior of the stopper 55.

In an exemplary embodiment, the seal member 102 sealingly interfaces with the piston-safety valve member 300 and has a through hole 324 in fluid communication with the safety valve 304. As such, during pretensioning, gas from the gas generator 36 can pass through the through hole 324 of the seal member 102 and the body opening 310 to the safety valve diaphragm 306 of the piston-safety valve member 300. As discussed above, when the central diaphragm portion 316 of the safety valve diaphragm 306 is intact (e.g., during normal pretensioning conditions below the predetermined pressure for rupturing the central diaphragm portion 316), gas from the gas generator 36 will be substantially obstructed from advancing further downstream to help push the pretensioner rod 53 through the tube 52.

The seal member 102 can have a generally cylindrical shape with a generally cylindrical outer surface, in one approach. In another approach, the seal member 102 can have a spherical shape with a spherical outer surface, or another appropriate shape and outer surface for sealing. As will be understood by those of skill in the art, the seal member 102 may be press-fitted or otherwise fitted inside the tube 52.

As shown in FIG. 10, the seal member 102 has a proximal end spaced from the gas generator 36 so as to define a gas chamber therebetween. The seal member 102 has a distal end that sealingly interfaces with the piston-safety valve member 300 and that is directed toward the stopper 55 and the pretensioner rod 53.

The stopper 55 is preferably made from aluminum, but could be made from another suitable material of sufficient strength, such as steel, other metal or metal alloy, or reinforced plastic. In an exemplary embodiment, the stopper 55 has an outer perimeter that substantially matches the perimeter of the non-recessed portion 206. The stopper 55 is adjacent the distal end of the piston-safety valve member 300 interfacing with the lip portion 318 of the member 300 along the interface 320. In an exemplary embodiment, the stopper 55 has an outer surface 326 that is curved and that interfaces with the lip portion 316. In one example and as illustrated, the outer surface 326 of the stopper 55 is configured as a semi-hemispherical surface.

Referring also to FIGS. 15A-15C, in an exemplary embodiment, a gap 328 is provided between the stopper 55 and an inner surface 330 of the tube 52. As will be discussed in further detail below, to prevent or in the event of an overpressure condition, fluid (e.g., gas from the gas generator 36) flowing downstream past the interface 320 of the lip portion 318 of the piston-safety valve member 300 and the stopper 55 can continue to flow downstream through the gap 328 and past the stopper 55. In one example and as illustrated in FIG. 15B, the outer surface 326 of the stopper 55 has notches 332 that form at least part of the gap 328 between the stopper 55 and the inner surface 330 of the tube 52. In another example and as illustrated in FIG. 15A, at least a portion of the outer surface 326 of the stopper 55 is substantially noncircular and the inner surface 330 of the tube 52 is substantially circular so as to form at least part of the gap 328 between the stopper 55 and the inner surface 330 of the tube 52. In another example and as illustrated in FIG. 15C, at least a portion of the outer surface 326 of the stopper 55 is substantially circular and the inner surface 330 of the tube 52 is substantially circular but having a larger diameter than the outer surface 326 of the stopper 55 to form the gap 328 between the stopper 55 and the inner surface 330 of the tube 52.

During pretensioning, the seal member 102, the piston-safety valve member 300, and the stopper 55 cooperate to transfer the energy from the increased pressure in the gas chamber 108 to the pretensioner rod 53. The pretensioner rod 53, in order to travel through the tube 52 and flex according to the curvature of the tube 52, is sized slightly smaller than the width of the tube 52. Thus, without the seal member 102 and the piston-safety valve member 300, gas from the gas generator 36 would flow past the pretensioner rod 53 in the space defined between the pretensioner rod 53 and the tube 52.

The seal member 102 defines a generally elastic structure, and may be composed of various materials known in the art, such as any suitable plastic or polymer (e.g., silicone, polyester, rubber, thermoplastic, or other elastic or deformable material). In an exemplary embodiment, the seal member 102 is made from silicone. Moreover, the seal member 102 may be die cast, forged, or molded from metal, plastic, or other suitable material. In one embodiment, the seal member 102 is formed using a two-cavity injection molding process. The generally elastic structure allows the shape of the seal member 102 to change slightly in response to pressure, thereby improving the sealing that it provides.

Referring to FIGS. 9-10, in operation, the gas generator 36 produces expanding gas that pressurizes the gas chamber, thereby enabling the seal member 102 and the piston-safety valve member 300 to forcibly drive the pretensioner rod 53 along the actuation path A. As the pretensioner rod 53 is driven through the tube 52, it engages the sprocket 56. More particularly, the pretensioner rod 53 engages the vanes 84 of the sprocket 56. Engagement of the pretensioner rod 53 with the sprocket 56 as the pretensioner rod 53 is driven by expanding gas in the direction of arrow A causes the belt spool 40 (shown in FIG. 3) to rotate, which in turn provides pretensioning.

Activation of the gas generator 36 enables the seal member 102 sealingly interfacing with the piston-safety valve member 300 to resist gas leakage. As previously mentioned, the seal member 102 is composed of a relatively elastic material. Therefore, pressurized gas within the gas chamber 108 causes the seal member 102 to expand, which helps prevent gas from escaping past the seal member 102 and the piston-safety valve member 300.

In addition, backpressure generated from the pretensioner rod 53 causes the seal member 102 to expand circumferentially outward due to compression of the seal member 102 against the piston-safety valve member 300, the stopper 55, and the pretensioner rod 53. The pretensioner rod 53 undergoes resistance as it engages the sprocket 56 during actuation, thereby generating backpressure on the stopper 55, piston-safety valve member 300, and the seal member 102. The circumferential expansion of the seal member 102 provides a tightened seal between the outer surface of the seal member 102 and the inner wall of the pretensioner tube 52. Accordingly, the seal member 102 with the piston-safety valve member 300 of the present invention is operable to retain a high seal pressure as well as maintain residual gas pressure within the tube 52.

During pretensioning of the seatbelt there can be a side-effect known as payback, where the tension on the seatbelt caused by the occupant during an event triggering pretensioning can rotate the spool in a direction opposite the pretensioning rotation. This rotation is transferred to the sprocket 56 and the driving elements, causing the driving elements to travel in the reverse direction within the tube 52. Payback can be counteracted by maintaining pressure in the tube 52, but this requires the gas generator 36 to fire for a longer period and additional propellant.

However, in an exemplary embodiment, the pretensioner system 44 described herein includes features configured to counteract the above described payback side-effect as an alternative to or in addition to maintained gas pressure. As described above, the pretensioner rod 53 is preferably made of a plastically deformable material, such as a polymer.

During actuation of the pretensioner system 44, the pretensioner rod 53 exits the tube 52 and contacts the vanes 84 of the sprocket 56, causing the sprocket 56 to rotate. As the pretensioner rod 53 continues past the sprocket 56 causing it to rotate, additional ones of vanes 84 will contact the side of the pretensioner rod 53, causing the pretensioner rod 53 to be compressed and deformed plastically in the area of interference between the vanes 84 and the pretensioner rod 53. This compression will also cause the pretensioner rod 53 to be compressed against the guide 90, creating a press-fit configuration of the pretensioner rod 53 between the sprocket 56 and the guide 90.

Additionally, the pretensioner rod 53 and guide 90 may be made from materials that will weld together at the end of the pretensioning stroke. For example, the materials of the pretensioner rod 53 and guide 90 may be selected such that heat generated from the friction between the pretensioner rod 53 and the guide 90 will cause the pretensioner rod 53 and guide 90 to become welded together along an interface W where the guide 90 and rod 53 contact each other. Once the pretensioner rod 53 and guide 90 are welded together, the pretensioner rod 53 will become locked and prevented or substantially limited from traveling back into the tube 52. The plastic deformation of the pretensioner rod 53 caused by the vanes 84 will prevent or substantially limit the sprocket 56 from rotating in the opposite direction, thereby preventing or substantially limiting payback.

The welding results from the relatively high heat and pressure generated by the system during actuation. For the pretensioner rod 53 and guide 90 to weld, the materials used for each are preferably in the same family. For example, if the guide 90 is nylon, then the pretensioner rod 53 is preferably nylon. Similarly, if the guide 90 is acetal, then the pretensioner rod 53 is preferably acetal. If the guide 90 is polypropylene, then the pretensioner rod 53 is polypropylene. It will be appreciated that other materials that will weld together under high heat and pressure could also be used. Moreover, it will be appreciated that some different types of materials can weld together.

Another side-effect that can occur during pretensioning is known as a low-resistance condition. This can occur when there is a relatively large portion of the seatbelt webbing that can be taken up or wound by the spool in response to actuating the pretensioner. For example, if there was extra slack in the seatbelt, this slack would be taken up and wound with lower resistance because it would not be acting on the occupant until the slack was taken up. In a low resistance condition, the backpressure of the driving elements is reduced. Reduced backpressure can result in a reduced ability of the sealing element to expand circumferentially against the inner wall surface of the tube in response to the backpressure. This can occur for any type of piston or seal that is configured to expand circumferentially in response to backpressure as part of its sealing process.

With reference to FIGS. 4, 9-10, and 14, to address the side-effect of a low-resistance condition of the pretensioner system 44, in an exemplary embodiment, the tube 52 includes a projection 120 extending within the tube 52 near an end (e.g., exit 89) of the tube 52 to form constriction portion 130 proximate to where the pretensioner rod 53 exits, thereby reducing the cross-sectional area of the tube 52 in a distinct location. That is, the opening diameter, width, or dimension(s) of the constriction portion 130 is smaller than the diameter, width, or dimension(s) of adjacent portions of the tube 52 portions, such as, for example, the portions of the tube 52 that are upstream from the constriction portion 130.

As will be discussed in further detail below, the recess 210 of the pretensioner rod 53 is aligned with the projection 120 along the actuating direction or path A such that during actuation and/or pretensioning, the recessed portion 208 of the pretensioner rod 53 is not obstructed by the projection 120. Moreover, the constriction portion 130 is sized such that there is enough space that at least the recessed portion 208 of the pretensioner rod 53 can travel past the constriction portion 130, but the stopper 55, the piston-safety valve member 300, and seal member 102 will be blocked from travelling past the constriction portion 130. When the stopper 55, piston-safety valve member 300, and the seal member 102 are blocked from advancing past the constriction portion 130, the constriction portion 130 provides additional backpressure. Accordingly, the seal member 102 will circumferentially or radially expand in response to this backpressure, thereby providing an improved seal in low-resistance conditions. This improved sealing will prevent or limit the potential for gas to escape from the tube 52 in low-resistance conditions.

The projection 120 defining the constriction portion 130 can be formed in a variety of ways and have a variety of shapes while providing the above described functionality. In one approach, shown in FIGS. 4, 9, and 14, the projection 120 is in the form of a crimp or bump 132 in the tube 52, such that the sidewall of the tube 52 maintains substantially the same thickness. The bump 132 is integrally formed with the tube as a monolithic structure, at least in the area of the constriction portion 130. Put another way, the bump 132 is not a separate component or material attached to the tube 52. The bump 132 protrudes into the tube 52, and has a corresponding depression on an outer surface of the tube 52. The bump 132 has a convex shape within the tube 52 and the depression has a corresponding concave shape.

In another approach, shown in FIG. 17, the projection 120 could be in the form of an increased thickness portion 138 that is integral with the tube 52. This is similar to the bump 132, but does not have a corresponding depression on outer surface of the tube 52.

In another approach, shown in FIG. 18, the projection 120 is in the form a separate piece or crescent 136 that is attached to the tube 52 within the tube 52. The crescent 136 a, 136 b, or 136 c can be attached via welding, adhesive, mechanical fasteners, or the like.

In another approach, shown in FIG. 19, the projection 120 could be in the form of a plate 140 that is inserted through an opening 142 formed in the sidewall of the tube 52. The plate 140 is removably inserted through the opening 142 and secured to the tube 52 via known securement mechanisms. In another approach, the plate 140 can be fixedly secured after insertion through the opening 142. The use of the plate 140 allows for different shapes and sizes and materials to be easily selected and installed, if desired.

In the above approaches, the projection 120 with the recess 210 of the pretensioner rod 53 aligned therewith may be disposed along an inboard portion of the tube 52 as illustrated in solid lines in FIGS. 4 and 9, or alternatively, may be disposed along an outboard portion of the tube 52 as illustrated in FIG. 14 and in dashed lines in FIGS. 4 and 9. Advantageously, in an exemplary embodiment, disposition of the projection 120 on the outboard portion of the tube 52 facilitates directing the distal end portion 204 of the pretensioner rod 53 away from the outboard portion of the tube 52 into engagement with the vanes 84 of the sprocket 56, thereby engaging the fully or solid side of the pretensioner rod 53 (e.g., sprocket 56 engaging side of the pretensioner rod 53 opposite the recess 210) during actuation. This can help to lock the pretensioner rod 53 with the sprocket 56 to prevent or reduce any translation of the pretensioner rod 53 in a direction opposite the actuating direction or path A. Alternatively, the projection 120 with the recess 210 of the pretensioner rod 53 aligned therewith may be disposed along an inboard portion, or any other side portion, of the tube 52.

As described above, the pretensioner rod 53 has the non-recessed portion 206 at its proximal end portion 202, where the non-recessed portion 206 has a larger diameter or cross-sectional dimension(s) than the recessed portion 208. In one approach, the non-recessed portion 206 has a diameter or cross-sectional dimension(s) that is larger than the width or cross-sectional dimension(s) of the tube 52 at the constriction portion 130. Accordingly, with the non-recessed portion 206 disposed upstream of the constriction portion 130, the constriction portion 130 will prevent the non-recessed portion 206 from passing.

In another approach, the non-recessed portion 206 can be smaller than the width or cross-sectional dimension(s) of the tube 52 at the constriction portion 130. With the non-recessed portion 206 being small enough to pass the constriction potion 130, it can pass beyond the constriction portion 130.

Another side-effect that can occur during pretensioning is known as an overpressure condition. This can occur, for example, when the retractor belt spool for some reason cannot pretension and the driving elements experience substantial resistance as they attempt to advance toward an end of the pretensioning stroke. This can cause a substantial increase in the pressure of the gas from the gas generator 36 that is advancing to expand and push the driving elements.

With reference to FIGS. 9-13, to address the side-effect(s) of an overpressure condition of the pretensioner system 44, in an exemplary embodiment, the tube 52 includes the sealing member 102 and the piston-safety valve member 300 to help vent gas to prevent or in the event of an overpressure condition as discussed above. In particular, when gas from the gas generator 36 is at or above a predetermined pressure that is associated with an overpressure condition, the sealing member 102 expands circumferentially outward due to compression of the seal member 102 against the piston-safety valve member 300. However, gas from the gas generator 36 can still pass through the through hole 324 of the seal member 102 and the body opening 310 of the piston body 302 to apply pressure to the safety valve diaphragm 306. Due to the excessive pressure of the gas at or above the predetermined pressure, the central diaphragm portion 316 of the piston-safety valve member 300 is configured to rupture (e.g., via thickness and choice of materials used to form the diaphragm) to allow the gas to flow therethrough downstream through the insert opening 312 in the channels 322 of the lip insert 308, and passed the stopper 55 through the gap(s) 328. The gas can continue to flow downstream between the spaces between the outer surface of the pretensioner rod 53 and the interior wall of the tube 52 and/or along the recess 210 of the pretensioner rod 53 to be vented through the exit 89 of the tube 52, or alternatively through the tube vent opening 400 that may be optionally formed through the tube 52 proximate the exit 89 and/or the projection 120. As such, gas from the gas generator 36 can be vented to address, mitigate, and/or prevent an overpressure condition.

Referring to FIGS. 20A-21D, alternative embodiments for the pretensioner rod 53, the piston-safety valve member 300, and the stopper 55 are provided. As illustrated, the recessed portion 208 of the pretensioner rod 53 may extend to the proximal-most end of the pretensioner rod 53 immediately adjacent to the stopper 55. As such, there is fluid communication between the stopper 55 and the pretensioner rod 53 along the recessed portion 208. Additionally, non-limiting alternative configurations for the piston-safety valve member 300 are illustrated in FIGS. 21A-21D in which the safety valve diaphragm 306 is mounted in the piston body 302 and the piston-safety valve member 300 is mounted directly on the stopper 55, for example, without the lip insert 308. As illustrated, the safety valve diaphragm 306 is disposed between the piston body of the piston-safety valve member 300 and the stopper 55. In these non-limiting alternative configurations, gas from the gas generator 36 passes through the through hole of the seal member 102 and the body opening of the piston body 302 to apply pressure to the safety valve diaphragm 306. Due to the excessive pressure of the gas at or above the predetermined pressure, the safety valve diaphragm 306 ruptures to allow the gas to flow downstream into and through the recessed portion 208 of the pretensioner rod 53 to be vented through the exit 89 of the tube 52, or alternatively through the tube vent opening 400. As such, gas from the gas generator 36 can be vented to address, mitigate, and/or prevent an overpressure condition.

As a person skilled in the art will readily appreciate, the above description is meant as an illustration of the implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation, and change, without departing from the spirit of this invention as defined in the following claims. 

The invention claimed is:
 1. A seatbelt pretensioning retractor assembly for use with a seatbelt webbing in a passenger vehicle, the seatbelt pretensioning retractor assembly comprising: a housing adapted for being mounted to a vehicle structure and having an interior cavity; a tube having an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing; a sprocket rotatably mounted to the housing and fixedly coupled to a spindle adapted for taking up the seatbelt webbing during a pretensioning; a driving element comprising a polymer rod having a proximal end portion that is disposed towards the gas generator and a distal end portion that is opposite the proximal end portion, and is configured to extend in a longitudinal direction from the proximal end portion to the distal end portion, wherein the polymer rod is disposed within the tube and is translatable through the tube in a first direction toward the sprocket in response to an actuation by the gas generator; a stopper coupled to the proximal end portion of the polymer rod; and a piston-safety valve member disposed between the gas generator and the stopper and configured to allow a gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure, the piston-safety valve member having a piston body and a safety valve operatively coupled to the piston body to allow the gas from the gas generator to pass through the piston body when the gas is at or above the predetermined pressure, the piston-safety valve further having a safety valve diaphragm that is between the piston body and the stopper.
 2. The seatbelt pretensioning retractor assembly of claim 1, wherein the piston body has a body opening formed therethrough that is in fluid communication with the safety valve diaphragm.
 3. The seatbelt pretensioning retractor assembly of claim 2, wherein the piston body has a wall that defines the body opening and that includes a shoulder portion at least partially surrounding the body opening, and wherein the safety valve diaphragm is disposed on the shoulder portion extending across the body opening.
 4. The seatbelt pretensioning retractor assembly of claim 3, wherein the safety valve diaphragm is disposed between the shoulder portion of the piston body and the stopper.
 5. The seatbelt pretensioning retractor assembly of claim 1, wherein the safety valve further comprises a lip insert that interfaces with the stopper and the safety valve diaphragm is disposed between the piston body and the lip insert, and wherein the lip insert has a lip insert opening formed therethrough that is in fluid communication with the safety valve diaphragm.
 6. The seatbelt pretensioning retractor assembly of claim 5, wherein the safety valve diaphragm is disposed between the shoulder portion of the piston body and the lip insert.
 7. The seatbelt pretensioning retractor assembly of claim 5, wherein the lip insert has a lip portion that contacts the stopper along an interface and that defines at least one channel that allows the gas from the gas generator to advance downstream from the interface between the lip portion and the stopper.
 8. The seatbelt pretensioning retractor assembly of claim 1, further comprising a seal member disposed between the gas generator and the piston-safety valve member.
 9. The seatbelt pretensioning retractor assembly of claim 8, wherein the seal member and the piston-safety valve member are cooperatively configured to drive the polymer rod through the tube in the first direction in response to the gas from the gas generator.
 10. The seatbelt pretensioning retractor assembly of claim 9, wherein the seal member sealingly interfaces with the piston-safety valve member.
 11. The seatbelt pretensioning retractor assembly of claim 8, wherein the seal member has a through hole in fluid communication with the piston-safety valve member.
 12. The seatbelt pretensioning retractor assembly of claim 1, wherein a gap is formed between the stopper and an inner surface of the tube that allows the gas from the gas generator to advance past the stopper.
 13. A seatbelt pretensioning retractor assembly for use with a seatbelt webbing in a passenger vehicle, the seatbelt pretensioning retractor assembly comprising: a housing adapted for being mounted to a vehicle structure and having an interior cavity; a tube having an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing; a sprocket rotatably mounted to the housing and fixedly coupled to a spindle adapted for taking up the seatbelt webbing during a pretensioning; a driving element comprising a polymer rod having a proximal end portion that is disposed towards the gas generator and a distal end portion that is opposite the proximal end portion, and is configured to extend in a longitudinal direction from the proximal end portion to the distal end portion, wherein the polymer rod is disposed within the tube and is translatable through the tube in a first direction toward the sprocket in response to an actuation by the gas generator; a stopper coupled to the proximal end portion of the polymer rod; and a piston-safety valve member disposed between the gas generator and the stopper and configured to allow a gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure, wherein the outer surface of the stopper defines at least one notch that forms at least part of a gap formed between the stopper and the inner surface of the tube wherein the gap allows the gas from the gas generator to advance past the stopper.
 14. A seatbelt pretensioning retractor assembly for use with a seatbelt webbing in a passenger vehicle, the seatbelt pretensioning retractor assembly comprising: a housing adapted for being mounted to a vehicle structure and having an interior cavity; a tube having an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing; a sprocket rotatably mounted to the housing and fixedly coupled to a spindle adapted for taking up the seatbelt webbing during a pretensioning; a driving element comprising a polymer rod having a proximal end portion that is disposed towards the gas generator and a distal end portion that is opposite the proximal end portion, and is configured to extend in a longitudinal direction from the proximal end portion to the distal end portion, wherein the polymer rod is disposed within the tube and is translatable through the tube in a first direction toward the sprocket in response to an actuation by the gas generator; a stopper coupled to the proximal end portion of the polymer rod; and a piston-safety valve member disposed between the gas generator and the stopper and configured to allow a gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure, wherein a gap is formed between the stopper and an inner surface of the tube that allows the gas from the gas generator to advance past the stopper, wherein an outer surface of the stopper is substantially noncircular and the inner surface of the tube is substantially circular so as to form at least part of the gap between the stopper and the inner surface of the tube.
 15. A seatbelt pretensioning retractor assembly for use with a seatbelt webbing in a passenger vehicle, the seatbelt pretensioning retractor assembly comprising: a housing adapted for being mounted to a vehicle structure and having an interior cavity; a tube having an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing; a sprocket rotatably mounted to the housing and fixedly coupled to a spindle adapted for taking up the seatbelt webbing during a pretensioning; a driving element comprising a polymer rod having a proximal end portion that is disposed towards the gas generator and a distal end portion that is opposite the proximal end portion, and is configured to extend in a longitudinal direction from the proximal end portion to the distal end portion, wherein the polymer rod is disposed within the tube and is translatable through the tube in a first direction toward the sprocket in response to an actuation by the gas generator; a stopper coupled to the proximal end portion of the polymer rod; and a piston-safety valve member disposed between the gas generator and the stopper and configured to allow a gas from the gas generator to pass therethrough when the gas is at or above a predetermined pressure, wherein a gap is provided between the stopper and an inner surface of the tube that allows the gas from the gas generator to advance past the stopper, and wherein the tube includes a projection extending extends within the tube adjacent to an exit at the second end to define a constriction portion that has an opening dimension smaller than an inside dimension of adjacent portions of the tube, and wherein the constriction portion is sized to prevent the stopper from passing therethrough, wherein the polymer rod has a recessed portion defining a recess that extends generally in the longitudinal direction, and wherein the recess is aligned with the projection in the first direction and the constriction portion is sized to permit the recessed portion of the polymer rod to pass therethrough.
 16. The seatbelt pretensioning retractor assembly of claim 15, wherein the tube includes a tube vent opening proximate the exit or the projection for facilitating venting the gas from the gas generator. 